Science

“Enormous amounts of virus in the upper throat area”

From the banal and essential question of a pediatrician where she should get masks and protective clothing from for herself and her employees to important details of the multiplication of the new corona virus – the spectrum of topics on Wednesday evening was so broad in the Langenbeck-Virchow-Haus.

“Coronavirus epidemic – first-hand information” promised the organizers, the Berlin Medical Society and the Berlin Microbiological Society.

Much more than 500 Spectators, mostly doctors, huddled in the hall to hear representatives of the Berlin health administration, the Robert Koch Institute and the emergency department of the Charité, but above all Christian Drosten, the world's most sought-after coronavirus expert from the Charité.

Little comforting

What he had to report about the latest research on Sars-CoV-2 was not very reassuring.

Contrary to what Drosten had suspected at the beginning of the epidemic – that this virus had infected the Sars pathogen of 2003 not only resembles, but would also behave like this – according to the latest research, multiply and spread “very differently”.

The Sars virus, according to Drosten, mainly reproduced deep in the lungs. Only there could it penetrate the cells, be multiplied there and mature into new, infectious virus particles. At the time, however, the researchers found hardly any viruses in the upper pharynx because it could not multiply there. And that makes a significant difference to the course of the epidemic, which was completely different for Sars than for Sars-CoV-2, Drosten explained: “The lungs are full of immune tissue, which means that there is an immediate feeling of illness.”

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Therefore, the patients quickly registered that they were getting sick, went to the doctor quickly, could be isolated quickly – even before the viruses had multiplied so much that they were present in the upper throat in sufficient quantities to be able to infect other people when coughing or sneezing. The fact that the patients only became infectious about a week after the first symptoms of the disease “extremely helped” to contain the epidemic.

“Great obedience from society” as a helpful factor in China

Because everyone had heard of Sars at some point, the patients came to the clinic quickly, and “together with a good clinic capacity, together with a great willingness to make decisions about home insulation and a great obedience of society ”, the outbreak had been successfully reduced to around 8000 cases and 800 Limit dead.

With Sars-CoV-2, however, the course of infection is different, there are “remarkable clinical differences,” says Drosten.

An investigation of 18 According to patients in China, unlike Sars, “extremely much virus” is in the upper throat area. “The highest virus concentration in the throat swab can be determined at a time when the symptoms are just beginning,” says Drosten.

More throat viruses than influenza

“You rarely see that much virus, not even with influenza.” In contrast, in the depths of the lungs, as measurements of sputum samples show, at the beginning of the course of the disease Sars-CoV-2 can be detected significantly less frequently, even less than was the case with Sars. However, because the feeling of illness is triggered in the lungs, where the immune cells sit and the cytokines sound the alarm, the patients have been infectious for a long time before they take their covid – 19 – notice disease at all.

Background to the coronavirus:

  • With face masks against the corona virus? What really protects against the transmission of germs
  • Study by Frankfurt researchers: Coronaviruses are probably also transmitted by healthy people
  • German coronavirus expert says: “We have to prepare for a pandemic”
  • The pathogen around the world: Interactive maps show how the corona virus has spread
  • Dramatic situation in northern Italy: “It is as if we were in Wuhan”

Meanwhile, Drosten also has an idea of ​​what could be the cause of this different behavior of the new corona virus: four additional building blocks (amino acids) in one Glycoprotein from the envelope of the virus. These building blocks created by random mutations are only found in Sars-CoV-2, not in Sars and not in its closely related viruses that circulate in bats.

You sit in a place where the protein will be cut up must, so that the viruses can “mature” and become infectious. “Something like this also occurs with influenza viruses and that is exactly what distinguishes low-pathogenic from highly pathogenic influenza viruses.”

Small molecular difference with big consequences

The reason for this, Drosten suspects, is that the glycoprotein of Sars-CoV-2 is also due to these four building blocks upper throat can be cut, not just deep in the lungs. “It is therefore already ripe from the cell”, regardless of whether it has proliferated in cells deep in the lungs or in the pharynx. Sars, on the other hand, relied on cutting enzymes (proteases) that only exist deep in the lungs. “The new virus does not need these proteases and can therefore replicate in the upper throat.”

As complex as the processes are, knowledge of the behavior of viruses has very practical consequences. It was important for the doctors present to hear that a swab in the upper throat, which is also routinely carried out in the case of influenza, is completely sufficient for the diagnosis of coronavirus. No patient has to be tortured so that the doctor can access samples from deeper areas of the airways.

In addition, research shows that with fever measurements at airports and Querying the symptoms of illnesses of travelers may identify some people who are already ill, but many infected people are likely to remain undetected.

Modell des die Krankheit Covid-19 auslösenden Coronavirus

model of the disease Covid – 19 triggering coronavirus Fig .: CDC

Using the data obtained from the patients examined in quarantine in Munich, Drosten was able to provide the assembled doctors with further information for the practice: “Ein symptom-free Covid – 19 – patient whose condition doesn't get worse, and a week in the hospital can be discharged. ” Because even if the researchers still detect virus in the throat swab with the very sensitive PCR method, according to the laboratory tests, these patients are no longer infectious.

“You will not be able to afford this if there is pressure on the beds”

That means the smears do not contain viruses more that are able to infect cell cultures. The Munich patients had become “virus-positive but clinically healthy long-term residents after one week” and had been in the hospital for two weeks until the PCR virus test had turned negative on two consecutive days.

“You will not be able to afford that when there is pressure on the beds,” said Drosten. They now have a scientific criterion to discharge clinically healthy patients after one week, despite the still positive PCR virus test. “The heads of the health authorities are still hesitant, but at some point the pressure on the beds will be so great that you will probably use this criterion.”

Another reassuring note: Apparently the virus is not spread through the stool: although viral genetics can be detected in stool samples from infected people, it was never used to infect cell cultures. “Good news regarding hospital hygiene and infection control,” said Drosten.

How important such information can become for German hospitals is shown by data published by Chinese researchers on mortality rates in the specialist journal “Lancet Global Health” on Wednesday. Accordingly, the mortality rate was higher in different regions of China, the more cases of disease per 10000 population gave. “That says something about the overloading of medical structures,” said Drosten. “People die because they can't get a hospital bed, a terrible correlation.”

And a warning for the hospitals to be prepared.

The hope is to delay the epidemic until summer

How high the case mortality rate can currently only be estimated – due to the still incomplete data situation. The data from China indicate that about three to four out of a hundred patients die. That would be a higher mortality rate than the Spanish flu of 1918 than worldwide 50 millions of people died.

“Something can't be right,” said Drosten. Apparently, many mild or even symptom-free cases of infection are not registered at all. Including this, the virologist, who pointed out that he was not an epidemiologist, estimated that the mortality rate was about 0.3 percent.

He hopes that Sars-CoV-2 will spread “slowly enough that you can make it into the summer” – a time when the viruses can make it due to increased UV -Radiation, dryness and the fact that fewer people are close together in poorly ventilated rooms are more difficult to spread. Drosten does not have the illusion that a vaccine can be developed in good time. “There won't be one, at the earliest next summer,” he predicts. Children – and that is very good news – can be infected and spread the virus, but they get sick much less often than adults. Even pregnant women would not have an increased risk, as is the case with influenza.

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